This invention relates to fusible elements for electrical apparatus such as vacuum fuses or interrupters.
Such apparatus can be subjected, among other conditions, to relatively high fault currents, which can be referred to as a short time high current condition, and to a prolonged overload current, which can be referred to as a long time low current condition. As can be verified on time-current curves, the cross sectional area of the fusible element is a major factor in determining the short time high current fusion condition and the length of the element is a major factor in determining the long time low current fusion condition.
In electrical apparatus such as vacuum fuses and/or interrupters there is an optimum spacing between electrodes which should not be exceeded and it is generally quite short. This does not afford much latitude for controlling time-current fusion characteristics by varying element length. Moreover, the nature of the materials generally required in such apparatus is such that they are good heat conductors. Therefore, any length variations that may be required would be difficult to accomplish in the available space.
Among the general objects of this invention is to control the heat to which the fusible element is subjected and, more specifically, to control the flow of heat from the fusible element.